MacFixIt.com has for years been a great source for troubleshooting info. It was recently purchased by CNET, but seems unchanged.

xlr8yourmac.com is another very useful resource, expecially regarding acceleration card issues, video card problems, etc.

MacInTouch is a great resource for information regarding issues and software, particularly updates and new software. Leopard FAQ page is great!

VersionTracker and MacUpDate are great sources for info and links to software and updates.

.Mac and Leopard

Remember to apply Login and Keychain update

Reported Mac OS X 10.5 Leopard Incompatible Software. Partial list below:

• From Apple: .Mac - Apple has a compatibility page for .Mac and Leopard, including the following note for Back to My Mac users: "Attention Back To My Mac users: In the coming weeks, we will be improving compatibility with home-based routers and various network environments. So if you find that you cannot access your remote Mac right away, please be patient as we work to improve the service."
  Backup 3.1.1
  Apple warns against using Backup 3.1.1 on Leopard. Upgrade to Backup 3.1.2 instead. Final Cut Pro 4
  According to Apple, Final Cut Pro 4 is not compatible with Leopard. Version 5.1.4 or later is required.
  iDVD 1, 2, 3, 4, 5, 7.0
  Not compatible. iDVD 6.0.4 and iDVD 7.0.1 are Leopard compatible.
  iPhoto 2
  Not compatible.
• FileMaker is mostly compatible, but with issues. Please see this page for versions 8.5 and earlier, this page for version 9 for info and update. Version 9.0v3 just released! Version 8.5v2 just released, Leopard compatible
• 4D is not yet officially compatible, but there is a partial workarounds here.
• The QuickBooks Pro 2007 for Mac R6 patch release is the latest for Leopard compatibility. R4 and earlier are not compatible.
  Quicken 2007 is Leopard compatible, earlier versions are not, according to Intuit. However, I've seen many reports of Quicken 2005 and 2006 working with no problems. YMMV
• Microsoft Office 2004 IS compatible!
• TextSoap 5.7.3 is compatible
• Daylite 3.5.2, Daylite Mail Integration 2.0.5, Billings 2.5.1. The current release versions are not Leopard compatible, but beta versions are available with fixes for Leopard.
• The Missing Sync Leopard-compatible release versions are available for Windows Mobile (4.0.2), Blackberry (1.0.3), and PSP (1.0.3). A Leopard-compatible beta version is available for Palm OS.
• Now Up to Date & Contact Client apps seem to work, but the server for Now Up to Date appears broken. QuickDay and QuickContact components don't work reliably. The Now Up to Date & Contact applications are working fine on Leopard."
• DEVONthink, DEVONagent
  The company has now released Leopard-compatible updates for DEVONthink Pro Office, DEVONthink Pro, DEVONthink Personal, DEVONnote, and DEVON agent.
• ThinkFree Desktop 3 is not yet fully compatible. ThinkFree is working on correcting the problems.
• FaxSTF not compatible. Update expected mid first quarter of 2008
• Photoshop 7 is not compatible.
• Adobe CS3 compatibility: Acrobat 8 Professional: Compatibility update scheduled for January 2008.
  Pro video applications including Premiere Pro CS3, After Effects CS3 Professional, Encore CS3, and Soundbooth CS3:
  Compatibility updates scheduled for December 2007.
  Photoshop Elements 4 and earlier: "Likely to encounter issues for which there is no resolution."
  Creative Suite 2 and earlier: "While older Adobe applications may install and run on Mac OS X Leopard, they were designed, tested, and released to the public several years before this new operating system became available. You may, therefore, experience a variety of installation, stability, and reliability issues for which there is no resolution. Older versions of our creative software will not be updated to support Mac OS X Leopard."
  Photoshop Lightroom Adobe has now released Lightroom 1.3 for Leopard compatibility. Versions 1.2 and earler are not compatible.
• Updates released for Eye Candy 5: Textures, Nature, and Impact; BlowUp; Snap Art; Exposure 1 & 2; and Xenofex 2. Previous versions are not compatible.
• Nikon says it plans to provide Leopard compatibility for the following products and their applicable software:
  - D-Series digital-SLR cameras that support either a IEEE 1394 or a USB connection.
  - Coolpix-series compact digital cameras that support a USB connection.
  - SUPERCOOLSCAN 9000 ED, SUPERCOOLSCAN 5000 ED, COOLSCAN V ED digital film scanners. SUPER COOLSCAN 8000 ED, SUPERCOOLSCAN 4000 ED, COOLSCAN IV ED digital film scanners.
  - Nikon released CaptureNX 1.3.1 to address a data loss bug when running on Leopard. Version 1.3.0, which has the bug, should not be used.
• MasterJuggler v3.0.4 is compatible.
• Many printers are not working well, especially Xerox printers.
• HP drivers built into 10.5 work well, but HP's drivers do not. Info here for print-only functionality. HP has issued a compatibility document here. HP All-in-One - Setup Instructions for Leopard. HP Photosmart Full Feature Software and Drivers - Mac OS X v10.5. HP has a beta of Officejet all-in-one installers available on its website. According to MacInTouch readers, "late beta" Leopard-compatible installers are available on HP's labyrinthine web site for OfficeJet and PhotoSmart all-in-one devices.
• Epson printers Some users are reporting problems with Epson printers, especially on PowerPC-based Macs running Leopard. Epson Printers information. New Stylus Pro drivers are available here.
• Lexmark printers will not have compatible drivers until "possibly March 2008"
• Scanning with OS X 10.5
• SilverFast 6.5.5r1 Scanning software NOT. Update coming.
• Dymo Label Software 7.7.1 with Leopard compatibility is now available.
• Some Brother QL and P-Touch Label Printers. See the Brother Leopard updates.
• Brother printers info here.
• Fujitsu SnapScan is very slow, in 1 report.
• Some Microtek scanners are not compatible, and Microtek is "evaluating and testing" and hope to have new drivers soon
• Canon supports the following printers in Leopard: 4400F, 8400F, 8600F, 8800F, 9950F, LiDE 25, LiDE 35, LiDE 60, LiDE 70, LiDE 90, LiDE 500F, LiDE 600F. Drivers available here.
• Canon has decided not to support the LiDE 80 under 10.5, but it is reported that if you redo the settings in the Canon scangear tool it will work normally.
• Canon CAPT printers The printing framework no longer works under Leopard.
• This list of Lexmark printers have support in Leopard.
• Nikon says it plans to provide Leopard compatibility for the following products and their applicable software:
  D-Series digital-SLR cameras that support either a IEEE 1394 or a USB connection.
  Coolpix-series compact digital cameras that support a USB connection.
  SUPERCOOLSCAN 9000 ED, SUPERCOOLSCAN 5000 ED, COOLSCAN V ED digital film scanners.
  SUPER COOLSCAN 8000 ED, SUPERCOOLSCAN 4000 ED, COOLSCAN IV ED digital film scanners.
• Retrospect 6.1.138 update for Leopard
  
• SilverKeeper is not compatible with Leopard yet.
• TechTool Pro: Micromat has released Version 4.6.1, which corrects problems with Leopard, including problems with eDrive. The Version 4.6.1 DVD will boot all currently shipping Macs.
• DiskWarrior 4.1 is Leopard compatible
• Application Enhancer (APE) 2.0.3 does not load, but does not cause problems. Older versions cause "blue screen" failures.
• Smart Scroll X A beta version of Version 2.7.5 brings Leopard compatibility for Cocoa applications only. Earlier releases are not compatible.
• The Missing Sync Leopard-compatible release versions are available for Windows Mobile (4.0.2), Blackberry (1.0.3), and PSP (1.0.3). A Leopard-compatible beta version is available for Palm OS.
• A Leopard-compatible release is now available for Deeper.
• SuperDuper 2.1.4 as "not yet compatible" (without details on any specific problems). A compatible version is currently in testing.
• The Leopard-compatible Cocktail 4.0 is now available. Previous versions are not compatible.
• The current release versions of Onyx and Maintenance are not compatible with Leopard. Initial beta versions for Leopard testing are available.
• Intech SpeedTools is compatible, but has appearance issues to be addressed.
• AppleJack 1.4.3 is not compatible
• Drive Genius is not compatible.
• Data Rescue II Prosoft has now released Version 1.2, which is fully compatible with Leopard. The previous version was only compatible with a Leopard-based Mac if booted from the product CD.
  
• Data Backup The Leopard-compatible Data Backup 3 is now available.
• Leopard Cache Cleaner 4.0.3 just released
• Intego lists current versions of all its Mac programs as Leopard compatible, including NetBarrier, ContentBarrier, and VirusBarrier
• iPartition 3.0.1 and iDefrag 1.6.5 include a workaround and should be safe in OS X 10.5
• TinkerTool is updated and compatible
• Toast Titanium 8.03 and Popcorn 3.0.2, just released, are now Leopard-compatible. Toast 7.1.3 resolves disc burning issues with Leopard. Previous versions are not compatible
• The StuffIt 11 contextual menu is again causing Finder re-draw issues. The solution is to remove the Stuffit Contextual Menu Item from the /Library/Contextual Menu Items folder and any StuffIt-related items from /Library/Frameworksor uninstall StuffIt altogether. Stuffit 12 may not have problems... no reports yet.
• VPN Tracker 5, now available, is Leopard compatible. VPN Tracker 4 is not and will not be made so.
• AOL for Mac OS X Version 10.3.7 is not currently compatible. AOL is working to fix issues.
• WeatherPop, WeatherPop Advance: not compatible, but working on it.
• D-Link AirPlus Extreme and several other third-party wireless cards with Mac-specific drivers are broken under Leopard.
• Sata Cards sold by Wiebetech.com need to have the latest firmware installed. Available on their website.

• Back up, ideally by cloning your Tiger drive to an internal or FireWire drive.
• Repair Permissions on the drive you will install to.
• If you will do an Update installation (the default, quickest and easiest, but can develop problems) make sure that you remove APE and any haxies, as well as input managers like SAFT, etc.
• If you Archive and Install, choose Preserve Users and Network Setting, for the easiest transition. This has been known to create issues, if there are incompatibilites or corrupt preference files. If you have issues, you can re-install not selecting Preserve Users and Network Setting, and re-create them.
• If you Erase and Install, you will be able to Migrate your files back to your Leopard disk. Again, incompatible or corrupt files can cause problems. You can also move data by hand, and reinstall your apps (with the app's installer) and recreate your User settings for the safest, if most time consuming installation.

  Each of these methods have been used with - and without - problems. I will report my personal experiences as time goes on, and any reports I find in the main section of this page.